[APM] Attempt to fix APMEventClient unit test (elastic#193049)

fixes elastic#190703

## Summary

The problem seems to be on the `void` keyword used when calling
`incomingRequest.abort()`.

I ran a few tests changing the `setTimeout` interval with and without
using the `void` keyword, and the test always passed when running
without it.

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/plugins/observability_solution/apm_data_access/server/lib/helpers/create_es_client/create_apm_event_client/index.test.ts

@@ -76,8 +76,9 @@ describe('APMEventClient', () => {
             resolve(undefined);
           }, 100);
         });
+
         void incomingRequest.abort();
-      }, 100);
+      }, 200);
     });
 
     expect(abortSignal?.aborted).toBe(true);